The majority of treatment programs targeting youth are based on a "12-step" model, a central aim of which, is to facilitate involvement in 12-step mutual-help groups, such as Alcoholics Anonymous (AA) and Narcotics Anonymous (NA). Research indicates that youth who attend AA/NA meetings have significantly better treatment outcomes. Furthermore, because AA and NA community networks are widely available and flexible enough to provide "acute" abstinence-specific support (e.g., through a sponsor) at times of high risk (e.g., evenings, weekends) as well as function as ongoing support systems at no cost, they hold promise as a useful adjunct to professional services in an increasingly cost-constricting, managed-care environment. However, little is known about youth AA/NA participation, in general, and what is known is derived solely from inpatient settings, which may not reflect current treatment reality as the system has transitioned to mostly outpatient care. Further, little is known about factors that influence AA/NA participation, or the specific change processes youth undergo during professional 12-step treatment. A prospective, process-oriented, design will be utilized to assess: 1) the extent to which youth (N=162;14-18 yrs) recruited from 12-steporiented outpatient treatment, attend, become involved in, and benefit from, AA/NA during a 12-month follow-up period;2) factors that influence adolescent AA/NA participation and related benefits;and, 3) the influence of treatment involvement on 12-step (e.g., disease-model beliefs), and common (e.g., self-efficacy, coping), processes of change and how these, in turn, relate to proximal (i.e., AA/NA involvement) and distal (i.e., substance use) outcomes. A secondary aim is to investigate staff 12-step referral practices and staff and parent attitudes toward AA/NA attendance for youth. Results will provide new information about the effectiveness of treatment as delivered to youth in current treatment contexts and supply developmentallyspecific knowledge that will inform 12-step facilitation efforts targeting youth.